An inorganic particle paste composition, which is configured by dispersing inorganic particles, such as conductive powder, ceramic powder, and so on, on a binder resin, is being used in order to gain diverse forms of plastic bodies. Most particularly, a fluorescent paste composition, which is configured by dispersing a fluorescent substance on a binder resin in the form of inorganic particles, is being used in LED or organic EL, and so on, and its demand has recently been increasing.
After being processed to a predetermined form by using methods, such as a deposition method using screen printing, Doctor Blade, and so on, a casting method for processing to a sheet form, and so on, the fluorescent paste composition, may be plasticized and then used.
As the binder resin being used in the fluorescent paste composition, a cellulose-based resin, such as ethyl cellulose having thixotropic properties, is generally used. However, the fluorescent paste composition, which is configured by dispersing a fluorescent substance on the cellulose-based resin, is not thermally decomposed unless it is plasticized at a high temperature. Therefore, there was a problem of a large amount of energy being required during the production process, or a problem of an extended plasticization time.
With respect to such problems, a method of using an acrylic-based resin, which can be degreased at a lower temperature as compared to the cellulose-based resin, is being considered. For example, a fluorescent paste composition using an acrylic-based resin is disclosed in Japanese Patent Laid-Open Publication No. H9-0129797. However, treatment of such fluorescent paste composition is difficult due to its strong adhesive property, which results from the acrylic-based resin. Although the adhesive property can be decreased by adjusting the added amount of the acrylic-based resin, since the viscosity of the fluorescent paste composition may be remarkably degraded accordingly, in case of dispersing high specific-gravity fluorescent substance, a problem of sedimentation or flocculation (or coagulation) of the fluorescent substance, which is also known as a decrease in storage stability, occurred.
Accordingly, by increasing the molecular weight (or mass) of the acrylic-based resin, the added amount of the acrylic-based resin may be reduced, and by increasing the viscosity of the fluorescent paste composition, the storage stability may be maintained,
In the Japanese Patent Laid-Open Publication No. 2003-257314, in order to enhance dispersibility of the fluorescent substance, a method of adding a compound having one or more carboxyl groups, such as Stearic acid, to a fluorescent paste composition is disclosed. It is disclosed herein that, by adding a compound having one or more carboxyl groups, the carboxyl group is adsorbed on the surface of the fluorescent surface causing surface potential to be neutralized or hydrogen bonding areas to be inactivated, and that, due to a volumetric effect of areas other than the carboxyl group, flocculation (or coagulation) may be controlled and the dispersibility of the fluorescent substance may be enhanced. However, when using this method, due to its difficulty in maintaining storage stability for a long period of time, sedimentation or flocculation (or coagulation) of the fluorescent substance occurred in some cases. Additionally, a fluorescent paste composition having low viscosity yielded a problem of a distinctive change in viscosity. As described above, a solution for realizing light transmittance and haze characteristics by ensuring the dispersibility of the fluorescent substance, thereby enhancing long-term storage stability of the fluorescent paste composition, is being required.